Marsdenia cundurango Reichenbach fil. belonging to the family Asclepiadaceae is a shrub of somewhat winding type growing naturally on and between mountains in the northwest of South America. Its bark is employed as an aromatic but bitter stomachic at the time of digestive disorder and/or anorexia, usually in the form of fluidextract (Commentary for the ninth Japanese Pharmacopeia)
The components of the bark of Marsdenia cundurango Reichenbach fil. include condurangogenin-A, condurangogenin-C and many other pregnane type compounds and their esters and glycosides, and the extraction, separation, structures and so on of them have been reported in, for example, the following documents. R. Tschesche et al., Tetrahedron, 21, p. 1777 (1965); 21, p. 1797 (1965); 23, p. 1461 (1967); and 24, p. 4359 (1968). M. Pailar et al., Monatshefte fur Chemie, 106, p. 37 (1975). Hiroshi Mitsuhashi et al., Chem. Pharm. Bull., 16, p. 2522 (1968). But details are still unclear in many respects.
As a result of study, the inventors of the present inventinon have found novel compounds represented by the above general formula (I) which have antitumor activity. The present invention has been completed on the basis of this finding.